Elbow prosthesis

ABSTRACT

An implantable elbow prosthesis (1) comprises an ulnar component (2) and a humeral component (3) wherein the head (21) of the ulnar component is designed in a bifurcated shape with two horns (22, 23) and the head (31) of the humeral component comprises a rotatable spindle (34) between two projecting flanges (32, 33). The joint component of the prosthesis is formed by arranging the head (21) of the ulnar component to engage with the spindle (34) of the humeral component. In each of the horns (22, 23) on the ulnar component (2) there is provided a groove (24, 25) which terminates in a respective blind hold (24, 25) on each horn (22, 23). A C-ring form of clip (4) connects the heads (21, 31) of the ulnar component and the humeral component, while maintaining the desired degree of freedom of movement for the elbow joint and a predetermined tolerance of movement. The clip (4) embraces the spindle (34) on the humeral component (3) with a clearance (5) between the arc (43) of the clip and the spindle and is locked to the ulnar component (2), the ends (41, 42) of the clip being inserted into the grooves (24, 25) on the horns (22, 23) of the ulnar component and engaging with the blind holes (26, 27). This ensures that the ulnar component (2) does not lose its grip on the spindle (34) of the humeral component, while at the same time the desired play is obtained in the actual joint connection, a vital circumstance for the functional characteristics of the prosthesis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns an elbow prosthesis for implantation in destroyedelbow joints, with an ulnar component and a humeral component intissue-compatible material, wherein the head of the ulnar component isdesigned in a bifurcated form with two horns, wherein the head of thehumeral component comprises a rotatable, replaceable spool or spindle ofa tissue-compatible and strong plastic material between two projectingflanges and wherein the joint component of the prosthesis is formed bythe head of the ulnar component being arranged to engage with therotatable spindle of the humeral component.

2. Description of Related Art

A large number of elbow prostheses are known in the literature and theart EP-0098 466 shows an elbow prosthesis wherein a fixed spindle on thehumeral component engages with a substantially cylindrical sliding piecein a cut-out on the spindle and wherein the sliding piece is anchored ona shaft which is attached to the ulnar component. The sliding piece isthereby rotatably mounted in the fixed spindle and is locked to it bymeans of a sleeve which has a C-shaped cross section and which is pushedover the spindle.

Furthermore EP-A-0 057 793 shows an elbow prosthesis of a similar kindwith a spindle-like element on the humeral component and a bifurcatedelement on the ulnar component. The object is to achieve an optimumjoining of the joint components and ensure stability, low loading andmobility with a minimum removal of bone tissue.

SUMMARY OF THE INVENTION

The basis for the present application is NO patent application no. 763136 which was submitted on 14, Sep. 1976 by one of the presentinventors and shelved on 4. Nov. 1977 without having been made generallyavailable. In this an elbow prosthesis is shown with a rotatable spindleor spool which engages with a bifurcated section of the secondprosthesis component and wherein the prosthesis components are attachedin the usual way to the medullary cavities in those bones which are tobe connected, i.e. the humerus and the ulna. This prosthesis has laterbecome known in practice and it will be referred to here in its entiretyas an example of the state of the art which forms the basis of thepresent invention.

The known prosthesis consists of several sizes of humeral components andseveral sizes of ulnar components with a common joint component, thusenabling for each patient the selection of the component size which isbest suited to the individual bones. The joint connection is free andthis prosthesis is therefore dependent on good ligaments and muscletendons in order to keep the joint in place. If the ligaments are notadequate, e.g. due to fracture and injury, the prosthesis will be ableto come out of joint.

Thus the object of the present application is to modify the knownprosthesis in such a way that the free joint connection can be blockedand convened to a so-called "semi-constrained" prosthesis which can alsobe used where the ligaments are not adequate and there is a risk of theprosthesis coming out of joint.

This object is achieved with an elbow prosthesis according to thepresent invention, characterized in that in each of the horns on theulnar component there is provided a groove which terminates in arespective blind hole on each horn, the blind holes being approximatelydiametrically opposite each other in relation to the ulnar component'sjoint centre, that the elbow prosthesis contains a C-ring-like clipganged to connect the heads of the ulnar component and the humeralcomponent while maintaining the desired degree of freedom of movementfor the elbow joint and a predetermined tolerance of movement, and thatthe clip embraces the spindle on the humeral component with a clearancebetween the arc of the clip and the spindle and is locked to the ulnarcomponent, the ends of the clip being inserted into the grooves on thehorn of the ulnar component and engaging with the blind holes. Furtherfeatures and advantages of the elbow prosthesis according to theinvention are described in the attached independent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The elbow prosthesis according to the invention will now be described inmore detail in connection with an embodiment and with reference to theattached drawing.

FIGS. 1a-1c show schematically the head of the ulnar component of theprosthesis seen from the rear, from the side and from above towards theopening between the horns respectively.

FIGS. 2a-2c show the clip of the present invention seen in a planarstate from the side and in a top view respectively and from the sideafter the clip has been bent into a C-ring shape.

FIGS. 3a and 3b illustrate the elbow prosthesis according to theinvention in an assembled condition, seen from the side and from therear along the axis of the ulnar component respectively and with theclip inserted.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

With reference to FIG. 1b it can be seen that the head 21 of the ulnarcomponent 2 forms a bifurcated structure with two horns 22,23, the endsof which project somewhat beyond a diameter in the fork arc. On theoutside of each horn 22,23 there are formed grooves 24,25 which eachterminate in a bore or blind hole 26,27 in each horn. Moreover in FIG.3a and 3b it is shown how the ends 41,42 of a C-ring-like clip 4 canengage with the head 21 of the ulnar component, the ends 41,42 of theclip being inserted into and in abutment with the grooves 24,25 on thehorn 22,23 of the ulnar component and engaging with the blind holes26,27 in the horns.

This C-ring-like clip 4 is illustrated in more detail in FIG. 2a-2c. Inthe example shown the clip 4 is in the form of an approximately 40 mmlong sheet component of, e.g. a titanium alloy and normally has a crosssection of approximately 1.5 by 3 min. The ends 41,42 of the clip areextended to form a semicircular sheet component with a diameter ofapproximately 5 mm. The clip 4 is bent into a C-ring shape asillustrated in FIG. 2c, the arc 43 in the C-ring being substantiallycomposed of a slightly wider section of the clip, while between thissection and the ends 41,42, the clip is made somewhat narrower in orderto provide optimum strength and elasticity. The inside of the arc 43 onthe clip 4 can be polished on those surfaces which can enter intocontact with the spindle 34 on the humeral component 3 in order toprevent unnecessary wear. When locking the prosthesis the ends 41,42 ofthe clip 4 are inserted into the grooves 24,25 in the horns 22,23 on theulnar component 2, as shown in FIGS. 3a and 3b, these grooves beingprovided approximately diametrically opposite each other in relation tothe joint centre of the ulnar component. The clip 4 is passed over thespindle 34 which is mounted on the humeral component 3 and locks it tothe ulnar component 2, the ends 41,42 of the clip engaging in the blindholes 26,27 on the ulnar component. The groove 24,25 in each of thehorns 22,23 has a width corresponding to that of the clip, thus ensuringthat after being attached the clip 4 will remain securely in placewithout the occurrence of any lateral movements which may cause wear.The arc 43 in the clip 4 is made wide enough to permit sufficientmobility between the humeral component 3 with the spindle 34 and theulnar component 2 and a suitable elasticity to ensure that the clip 4 issecurely attached when its end 41.42 have engaged with the blind holes26,27 on the horn 22,23 of the ulnar component. A humeral component 3has a head 31 that includes a rotatable spindle 34 between twoprojecting flanges 32 and 33. The ulnar component 2 is thereby securelyattached to the humeral component 3 and holds the spindle 34 of thehumeral component in a secure grip, while at the same time some play ispermitted in the actual joint connection, a vital circumstance for thefunctional characteristics of the prosthesis. The mounted prosthesiswith the clip in place is illustrated in FIGS. 3a and 3b and FIG. 3aclearly shows the clearance 5 between the spindle 34 and the arc 43 ofthe clip and also that the ends of the horns 22,23 on the ulnarcomponent 2 project somewhat above a diameter on the spindle 34, e.g.approximately 5 mm beyond this diameter. This means that the clip 4cannot work loose or fall off unless it breaks. Any tension load on theclip 4 will in fact act outwards through the middle of the arc 43 of theclip and the tension load will therefore only help to further tightenthe clip. The ends of the clip will never be able to be pushed out ofthe bores by the forces acting on the prosthesis during use.

The clip and the other metal components in the prosthesis are made oftissue-compatible material, preferably titanium alloy, as are the othermetal components in the prosthesis, thus making the prosthesis verystrong and durable, e.g. it has a tensile strength of several thousandkilonewton.

The ulna component 2 and the clip 4 are designed in such a manner thatthe clip can be fitted at any time in the course of an operation, evenafter the actual prosthesis has been cemented into the bones and thejoint put in place. Similarly, the clip can also be easily removed if itsubsequently proves to be unnecessary, possibly by means of a subsequentoperation.

Thus by means of the present invention an elbow prosthesis has beenprovided which can also be used where the ligaments are not adequate,thereby eliminating any risk of the prosthesis coming out of joint.

We claim:
 1. An elbow prosthesis for implantation in destroyed elbowjoints, with an ulnar component and a humeral component of atissue-compatible material, wherein the head of the ulnar component isdesigned in a bifurcated form with two horns, wherein the head of thehumeral component comprises a rotatable, replaceable spindle of atissue-compatible and strong plastic material between two projectingflanges, and wherein the joint component of the prosthesis is formed bythe head of the ulnar component being arranged to engage with therotatable spindle of the humeral component,characterized in that in eachof the horns on the ulnar component there is provided a groove whichterminates in a respective blind hole on each horn, the blind holesbeing approximately diametrically opposite each other in relation to thejoint centre of the ulnar component, that the elbow prosthesis includesa C-ring-like clip arranged to connect the heads of the ulnar componentand the humeral component while maintaining a desired degree of freedomof movement for the elbow joint and a predetermined tolerance ofmovement, and that the clip embraces the spindle on the humeralcomponent with a clearance between an arc of the clip and the spindleand is locked to the ulnar component by ends of the clip being insertedin the grooves on the horns of the ulnar component and engaging with theblind holes.
 2. An elbow prosthesis according to claim 1, characterizedin that the clip is made of a tissue-compatible material, preferablytitanium alloy.
 3. An elbow prosthesis according to claim 2,characterized in that the ends of the clip are formed as a sheet-shapedextension with an approximately semicircular shape and with a maximumwidth of about 5 mm.
 4. An elbow prosthesis according to claim 3,characterized in that the grooves in the horn of the ulnar componenthave a width corresponding to a width of the clip between the arc of theclip and its ends.
 5. An elbow prosthesis according to claim 4,characterized in that the ends of the horns on the head of the ulnarcomponent each project beyond a diameter of the spindle on the humeralcomponent when the prosthesis is mounted, preferably by approximately 5mm.
 6. An elbow prosthesis according to claim 5, characterized in thatthe clip is arranged to be installed or removed during or after theinstallation of the prosthesis.